The present invention relates in general to shaft sealing and packing arrangements for accommodating a rotating shaft, and in particular to a new and useful liquid sealed shaft seal which utilizes an axially movable piston which moves into different positions depending on whether the shaft to be serviced by the shaft seal is rotating or not.
Seals of this kind are known under the designation centrifugal-type seal. In such seals, during the rotation of the shaft, a seal disc firmly secured to the shaft produces a pumping effect, namely increases the radial pressure in a stationary seal chamber surrounding the seal disc, of sealing liquid which is supplied to the chamber, so that a ring of rotating sealing liquid is formed at the rotating seal disc. The inner diameter of this rotating ring of sealing liquid, at either side of the rotating seal disc, adjusts to a radial level corresponding to the state of equilibrium between the outer space and inner space pressures of the seal. Such a seal is wear-free and without any significant leakage of sealing liquid into the inner space. At low speeds and at standstill of the shaft, however, the seal becomes ineffective since the needed centrifugal force is absent.
To overcome this drawback, centrifugal-type seals have been combined with floating seal rings, namely radially displaceable cylindrical bushings which are sealed against the housing and form with the shaft an axial sealing gap filled with sealing liquid. This, however, cannot prevent considerable leaks of sealing liquid to the inner space either, since a floating ring seal requires a certain excess pressure of the sealing liquid even at standstill or low speeds of the shaft, which excess pressure must be controllable from the outside because of the varying gas pressures.
Sealing liquid leakage, both at standstill and at any speed, can be reduced to insignificant amounts by means of so-called slide ring seals in which a seal disc firmly secured to the shaft is provided, and one or more slide rings are axially urged into contact with the disc by a resilient sealing element. Cooling and sealing is effected with a sealing liquid supplied between the slide rings. In spite of that, however, high temperatures occur in the extremely narrow sealing gap at high speeds, leading to a decomposition of the sealing liquid and destruction of the slide rings, thus making the packing ineffective.